Some radiators hot, some lukewarm

[FooManChu]

Hi Folks

I have recently purchased a house with a 20 year old CH &HW system. The boiler is a ThornEMI (not certain of model although I can find out) and from what I have read on here, it appears to be a Primatic system (single header tank located above the Cylinder in the bathroom). Now, I have 10 rads with 4 hot and the rest barely lukewarm.

I've traced the hot pipe coming from the boiler into the first rad and traced the outlet from this rad to the next rad and its hot. The outlet from the second rad is also hot and it appears that the pipe then returns to the boiler. However, the other rads appear to be on a second section from the boiler and tracing this pipe to the first rad from the boiler is hot (it also goes to a second rad via the inlet pipe which is also hot). However, the outlet for the first rad is barely lukewarm and this feeds to all the other "lukewarm" rads. I've meddled (yes, not professionally I'm afraid) with balancing but it has made no difference (no, I didn't use thermometers which is wrong for an amateur). Another issue is that some of the valves leak so I intend to kill 2 birds with a single stone and replace them with TRV's(I think you pro's call them that).

I've:-

a) Checked the single header tank which appears to contain and refill (when using hot water) with water.

b) Blead each rad in turn (thus finding that some valves leak badly) which has not resolved the problem

c) Attempted to balance the system albeit rather DIY'shly. Again, not solved the problem.

Questions?

1) How can I drain this kind of system and is it easy to refill (in order to replace the leaky valves and maybe flush each radiator incase any contains gunge).

2) I think that (from reading info. on this forum) that I cannot add rust prevention fluid to this kind of system, correct? If so, what prevents the rads from corroding? (I guess the answer is nothing, right?).

3) What would probably be the cause of the initial problem of some rads hot, some cold? Cold are downstairs and up if that helps.

Any help whatsoever from the experts will be greatly appreciated.

Regards

AH

 

[kevplumb]

have you got a pump and if so is it working

 

[FooManChu]

Hello KevPlumb

I do have a pump and I think it is working. The pump is located in a rather difficult position between the boiler case and the wall (about a pump width between them. When the casing of the boiler housing touches the pump, a small vibration can be heard and I guess this may indicate that the pump is functioning but other than take it apart, I guess I am not totally certain that it is working.

Is there any special way to determine if a pump is working KevPlumb?

Regards

AH

 

[kevplumb]

undo the screw in the middle and insert screwdriver

 

[FooManChu]

Hi KevPlumb

Thanks for replying so promptly.

I will try your suggestions and get back to you.

If the pump works and I put a screwdriver in, won't this break something?

Anyway, I'll try it and see if I get any resistance.

Do you have any comments on my other questions Kev?

Regards

AH

 

[FooManChu]

Hi KevPlumb

I think I'll leave this now until the weekend. The boiler is contained within a sideboard (nicely boxed around it to disguise it) with adequate ventilation. Upon a partial removal of this sideboard I have located a second pump which appears to also be working (i've put my hand on it and it is humming with a small vibration). I cannot get to it that well until I can dismantle the rest of the sideboard around the boiler. The other pump is, as I've mentioned, in a fantastic position squashed up against a wall as well as the boiler casing. So at the weekend I will investigate further to determine if both pumps are working. It would appear that one pump serves only 2 radiators that are hot. The other serves 8 in which only 2 are hot and the rest are barely lukewarm. Not certain why I have 2 pumps as neither are for the hot water and only for the central heating. The hot water is clearly gravity fed as its very weak in the bathroom.

Would it be possible for me to use some of that "Freeze" solution to freeze the pipes either side of a radiator in order to remove the radiator and fit a TRV to it? Is this "Freeze" spray any good?

Regards

AH

 

[kevplumb]

yes it works but it costs
if your doing a few it might be worth hiring an electric freezer

 

[FooManChu]

Hi KevPlumb

I guess this all depends on how well the first attempt goes. I'll asses each one as I go. I did not know there was such a thing as an Electric freezer but that's good to know. I've read somewhere that the freeze aerosols are around a tenna and I have no idea (yet) how much I'll need for each rad. This may be a better way around as I've still not located the drain valve on the system and the only valve I can see that I can connect a hose to is on the boiler itself. BTW, I checked the header tank last night to be certain nothing was blocked there and it appears to be clear (except for a pair of pliers that someone must have once dropped in the tank as they are now more like a relic from the Titanic. This has produced some rust grains which I may be able to siphen out somehow.

Thanks for the prompt response once again KevPlumb

Regards

AH

 

[FooManChu]

Hi KevPlumb

Ok, I've checked the pump which appears to power 8 of the rads, removed the centre screw (some red'ish water dripped out), switched it on again and inserted a screwdriver. I felt the pump spinning and the fins touching the screwdriver. I've also removed the first radiator fed from the boiler which this pump seems to power, taken it outside, flushed it with a hose (black gunge and red water came out of it for a while) and I've refitted the rad (I love it the way pipes leak once you've disturbed them) and I also turned on both valves before fitting and water was flowing from them both. I've now switched on the system. I've got pretty much the same problem with the water from the pump being RED hot (as well as the pump itself) and the water leading into the first rad RED hot (it also branches to a second rad which is hot also) and the rad itself is hot near the top, lukewarm near the bottom thus the outlet pipe is also lukewarm. I've blead the rad and there is no air in it that I can detect (there was after refitting naturally) so I am stuck again.

What can I try next to determine what the problem could be?

Regards

AH

 

[kevplumb]

sounds like the pump impeller may be broken
could try turning the speed up other than that strip the pump

 

[FooManChu]

Hi KevPlumb

I've switched off all rads today (closed valves at both ends) apart from one rad upstairs. The rad upstairs remained cold. Could there be a blockage as well? If I strip the pump and find the impeller is indeed broken, can these be replaced or is it as I think, replace the entire pump? If its the latter, it may well be easier and time saving to just try a new pump anyhow.

Regards

AH
PS how come your location has changed from Faulklands to Tailand? An international plumber?

 

[kevplumb]

to bl**dy cold mate
you might as well replace as you wont get bits